Learn more about using open source R for big data analysis, predictive modeling, data science and more from the staff of Revolution Analytics.

February 20, 2009

Subway riders in large cities: Making the simple impenetrable

Good magazine has a chart intended to make the point that public transit in US cities lags behind that of large cities elsewhere in the world. It's an awful chart. Any chart that takes a good three minutes of staring to figure out what it was trying to represent isn't doing its job. Let's count the ways it fails:

It doesn't fit on the screen (or my screen, at least). It's impossible to compare the cities when you have to scroll around. I had to view the JPG -- a poor choice of format for any chart -- and use Firefox's image zoom feature to see it all in context.

The length of the trains is clearly supposed to represent something, but what? It's none of the statistics listed on the yellow box on the right hand side, clearly. All of the trains extend off the left side of the chart, so I assume it's a scale that doesn't begin at zero. New York's train doesn't fit on the chart at all. It takes some searching, but a tiny legend at the bottom-right reveals that it represents total system track length. Why this is a more important measure to devote to charting than, say, city population is beyond me. "System Track Length" itself is a vague concept: Paris's chart clearly doesn't include the 365 miles of the RER, for example.

London's Tube, one of the oldest, largest, and most-ridden subway systems isn't included. How were the included cities chosen? The title says "The most used subway systems in the US and the World". The selected cities suggest otherwise.

The city statistics in the yellow boxes on the right don't line up with the corresponding chart elements for the city.

Using the people to represent the number of riders (actually millions of rides per day -- that legend is a bit easier to find) is overly cute. Also for some reason Chicago's riders are packed in tightly, but there are many unexplained gaps between Tokyo's riders. I assume this is not meant to be meaningful.

It's a shame, because the chart does make a good point in a bad way. Mass transit is underutilized in the US. Funding and culture certainly has something to do with it, but my personal experience is that the subway systems in the US are too difficult for newcomers to use. The Metro, the Tube and Tokyo's Subway are all clearly signposted, have easily-understood maps (the fact that they are schematic, not geographical like the NYC Subway map, helps), and have fare systems that are easily understood and implemented by visitors. By contrast, I used San Francisco's BART for the first time yesterday. I wanted to take a trip from my hotel near the Embarcadero station to SFO Airport, which I imagine is a common task for a visitor. There are no live ticket sellers, the only option is a machine. But to use the machine, you have to first insert an amount of money -- any amount will apparently do -- and then issue a ticket. But here's the kicker -- nowhere is the user told how much a ticket costs! I had to go ask at the information desk (hosting the only live employee in the hall) and then return to the machine before I forgot the cost. How about a "Ticket to SFO" button on the machine? Would that be so hard?

OK, so I used this chart as a thinly-veiled excuse to rant. Rant over. It's still an awful chart, though.